1. Field of the Invention
The present invention relates to a fuel cell formed by stacking a membrane electrode assembly and separators together. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes a solid polymer electrolyte membrane, an anode provided on one side of the solid polymer electrolyte membrane, and a cathode provided on the other side of the solid polymer electrolyte membrane. The solid electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is sandwiched between separators to form a power generation cell (unit cell). Generally, several tens to hundreds of power generation cells are stacked together to from a fuel cell stack, e.g., for use in a vehicle.
In some cases, the membrane electrode assembly is an MEA having different sizes of components where a gas diffusion layer of one of the electrodes has a plane size which is smaller than that of the solid polymer electrolyte membrane, and a gas diffusion layer of the other of electrodes has the same plane size as that of the solid polymer electrolyte membrane.
Normally, in the fuel cell stack, a large number of membrane electrode assemblies are stacked together. In order to reduce to the production cost, it is desired to adopt inexpensive structure of the membrane electrode assembly. Therefore, in particular, various proposals have been made for reducing the used amount of the solid polymer electrolyte membrane, and simplifying the structure.
For example, a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2013-098155 has a membrane electrode assembly including a solid polymer electrolyte membrane and a first electrode and a second electrode provided on both sides of the solid polymer electrolyte membrane. Each of the first electrode and the second electrode has an electrode catalyst layer and a gas diffusion layer. The outer size of the first electrode is smaller than the outer size of the second electrode. A resin frame member is provided around the solid polymer electrolyte membrane.